Rinse the buckwheat, then place it in a saucepan with 2 cups of water and the stock cube.
Bring to a boil, then reduce the heat and simmer for 15–20 minutes, until the liquid is absorbed. Cover and let it rest.
Meanwhile, chop the onion and red pepper.
Heat a little oil in a pan and gently cook the onion, capers, chilli flakes, red pepper, and herbs for about 8 minutes, until softened.
Add a splash of water and the lemon juice, then stir in the chopped greens. Cover and let them steam for about 5 minutes.
Add the seafood and warm through gently. (If using raw seafood, cook for 3–5 minutes until just done.)
In a large bowl, combine the buckwheat with the seafood mixture and lemon zest.
Taste and adjust seasoning if needed.
Serve warm with an extra squeeze of lemon and a sprinkle of fresh parsley.